Google-assistant integration dialog flow: List not working in google assistant - actions-on-google

Question

I am sending both simple_response and list_card in messages to dialog flow but google assistant stops responding
After response from webhook my json in dialog flow looks like:
{
"id": "c8d70d1a-fe39-4417-94a8-f586db516961",
"timestamp": "2017-12-04T09:40:11.687Z",
"lang": "en",
"result": {
"source": "agent",
"resolvedQuery": "Popular Science",
"action": "searchWithCategory",
"actionIncomplete": false,
"parameters": {
"any": "Popular Science"
},
"contexts": [
{
"name": "filter",
"parameters": {
"item": "library",
"any.original": "Popular Science",
"any": "Popular Science"
},
"lifespan": 5
}
],
"metadata": {
"intentId": "12a29272-a89d-4fae-b4f8-497f75f6f1d1",
"webhookUsed": "true",
"webhookForSlotFillingUsed": "false",
"webhookResponseTime": 331,
"intentName": "searchStoriesWithCategory"
},
"fulfillment": {
"speech": "We have found 2 articles for you",
"source": "webhook",
"displayText": "We have found 2 articles for you",
"messages": [
{
"speech": "We have found 2 articles for you",
"type": 0
},
{
"textToSpeech": "We have found 2 articles for you",
"type": "simple_response",
"platform": "google"
},
{
"title": "We have found 2 articles for you",
"type": "list_card",
"items": [
{
"image": {
"url": "http://image1.example.png"
},
"optionInfo": {
"synonyms": [
"P"
],
"key": "PubMed: Swine Flu"
},
"description": "PubMed: Swine Flu",
"title": "PubMed: Swine Flu"
},
{
"image": {
"url": "http://image1.example.png"
},
"optionInfo": {
"synonyms": [
"L"
],
"key": "Local Level - Resolving community Issues"
},
"description": "Local Level - Resolving community Issues",
"title": "Local Level - Resolving community Issues"
}
],
"platform": "google"
}
]
},
"score": 1
},
"status": {
"code": 200,
"errorType": "success",
"webhookTimedOut": false
},
"sessionId": "002e6053-78c1-49ee-a9dc-76df21fac798"
}